This invention is an improvement over the gap measuring device disclosed and claimed in my U.S. Pat. No. 4,549,207 issued on Oct. 22, 1985. As disclosed in my prior patent, highly stressed aerospace vehicle structures such as the wings of high speed aircraft, require enhanced life expectancy against fatigue. In the manufacture of such structures, several layers of panels are fastened together by means of fasteners inserted through holes drilled in the panels. The space (or gap) between multilayered panels at the location of each fastener must be reduced to acceptable values before the fastener is tightened, since out of tolerance gaps will create localized stress regions when the panels are drawn together by torquing down the threaded fastener bolts. To prevent the occurrence of these stresses, the gaps between the marting panels are measured, and if necessary, shims are inserted to eliminate, or at least reduce the gap to an acceptable level. The gaging of the gaps for the preparation of the shims is made through the fastener holes. It it the object of the present invention to accomplish the same results disclosed in my prior patent, but with improved accuracy and efficiency.
My prior patented system utilized a rigid borescope having fiber optic illumination of the panel edges surrounding the fastener hole. A right angle prism at the tip, or probe end of the borescope permitted the viewing of the panel edges and the sensing of the gap between the panels. Precision eccentric sleeves were required as guides to provide centering of the borescope probe end within the fastener holes, different size eccentrics being required for different sizes and shapes of holes. In accordance with this invention, I provide a spring biased, conically tapered probe guide which serves automatically to guide the probe end of the borescope into the center of the hole, and can function for a wide variety of fastener holes with ease of use and precision results.